Biktarvy is indicated in the U.S. as a complete regimen for the
treatment of HIV-1 infection in adults who have no antiretroviral
treatment history. Biktarvy is also indicated to replace the current
antiretroviral regimen in those adults who are virologically suppressed
on a stable antiretroviral regimen for at least three months.
Virologically suppressed adults must have no history of treatment
failure and no known substitutions associated with resistance to the
individual components of Biktarvy. Biktarvy carries a Boxed Warning in
its U.S. product label regarding the risk of post-treatment acute
exacerbation of hepatitis B. See below for Important Safety Information.

“Maintaining virologic suppression, even in the setting of resistance to
certain classes of HIV medicines, when switching to Biktarvy, speaks to
the versatility of Biktarvy,” said John McHutchison, AO, MD, Chief
Scientific Officer and Head of Research and Development, Gilead
Sciences. “These data add to the growing body of evidence supporting
Biktarvy as a single tablet regimen that can be used in a wide range of
clinical settings.”

Participants in two Phase 3 Biktarvy switch studies (Studies 1844 and
1878) were followed through two years of therapy in the open-label
continuation of these studies past the Week 48 primary endpoints.
Documented resistance to study drugs was exclusionary; for the purposes
of this retrospective analysis, archived preexisting HIV-1 drug
resistance was assessed by historical genotypes and retrospective
baseline proviral DNA genotyping. Among adults who switched to Biktarvy
from DTG/ABC/3TC or a boosted protease inhibitor (PI)-based regimen,
high rates of virologic suppression were observed in the overall
population (n=561/570; 98 percent) as well as the population with
preexisting drug resistance (n=155/159; 97 percent), including those
with archived M184V/I (n=42/44; 95 percent). No patients developed
treatment-emergent resistance during the course of the study.

Poster 3362: High Level of Pre-Existing NRTI Resistance Prior to
Switching to Biktarvy

This ongoing, randomized, double-blind Phase 3 study (Study 4030)
evaluated 565 virologically suppressed adults who switched 1:1 from a
regimen of DTG+F/TAF or DTG+F/TDF to DTG+F/TAF or Biktarvy for 48 weeks.
Participants with any documented nucleoside reverse transcriptase
inhibitor (NRTI), non-nucleoside reverse-transcriptase inhibitor
(NNRTI), and protease inhibitor (PI) resistance were allowed to enroll;
patients with documented INSTI resistance were excluded. Archived
preexisting HIV-1 drug resistance was assessed by historical genotype
and retrospective baseline proviral DNA genotyping. In the study, 14
percent (n=78/565) of participants had NRTI resistance known or
suspected at screening. This increased to 24 percent (n=138/565) using
historical data combined with additional baseline proviral HIV-1 DNA
genotyping. In this pooled, blinded interim analysis, 99 percent
(n=557/562) of all participants with any post-baseline visit and 99
percent (n=220/222) of participants with resistance to any class of ARV,
including those with archived M184V/I (n=79/81; 98 percent), had
undetectable viral load (HIV-1 RNA <50 copies/mL) with no emergent drug
resistance.

The efficacy and safety profile of Biktarvy in patients with preexisting
resistance to its components has not been established; its use in these
populations is investigational. Biktarvy does not cure HIV infection or
AIDS.

IMPORTANT U.S. SAFETY INFORMATION AND
INDICATION FOR BIKTARVY

BOXED WARNING: POST TREATMENT ACUTE EXACERBATION OF HEPATITIS B

Severe acute exacerbations of hepatitis B have been reported in
patients who are coinfected with HIV-1 and HBV and have discontinued
products containing emtricitabine (FTC) and/or tenofovir disoproxil
fumarate (TDF), and may occur with discontinuation of Biktarvy.
Closely monitor hepatic function with both clinical and laboratory
follow-up for at least several months in patients who are coinfected
with HIV-1 and HBV and discontinue Biktarvy. If appropriate,
anti-hepatitis B therapy may be warranted.

Contraindications

Coadministration: Do not use Biktarvy with dofetilide or
rifampin.

Warnings and precautions

Drug interactions: See Contraindications and Drug
Interactions sections. Consider the potential for drug interactions
prior to and during Biktarvy therapy and monitor for adverse reactions.

Immune reconstitution syndrome, including the occurrence
of autoimmune disorders with variable time to onset, has been reported.

New onset or worsening renal impairment: Cases of acute
renal failure and Fanconi syndrome have been reported with the use of
tenofovir prodrugs. In clinical trials of Biktarvy, there have been no
cases of Fanconi syndrome or proximal renal tubulopathy (PRT). Do not
initiate Biktarvy in patients with estimated creatinine clearance
(CrCl) <30 mL/min. Patients with impaired renal function and/or taking
nephrotoxic agents (including NSAIDs) are at increased risk of
renal-related adverse reactions. Discontinue Biktarvy in patients who
develop clinically significant decreases in renal function or evidence
of Fanconi syndrome.

Renal monitoring: Prior to or when initiating Biktarvy and during
therapy, assess serum creatinine, CrCl, urine glucose, and urine protein
in all patients as clinically appropriate. In patients with chronic
kidney disease, also assess serum phosphorus.

Lactic acidosis and severe hepatomegaly with steatosis: Fatal
cases have been reported with the use of nucleoside analogs, including
FTC and TDF. Discontinue Biktarvy if clinical or laboratory findings
suggestive of lactic acidosis or pronounced hepatotoxicity develop,
including hepatomegaly and steatosis in the absence of marked
transaminase elevations.

Adverse reactions

Most common adverse reactions (incidence ≥5%; all grades)
in clinical studies were diarrhea (6%), nausea (5%), and headache (5%).

Drug interactions

Prescribing information: Consult the full prescribing
information for Biktarvy for more information on Contraindications,
Warnings, and potentially significant drug interactions, including
clinical comments.

Enzymes/transporters: Drugs that induce P-gp or induce
both CYP3A and UGT1A1 can substantially decrease the concentration of
components of Biktarvy. Drugs that inhibit P-gp, BCRP, or inhibit both
CYP3A and UGT1A1 may significantly increase the concentrations of
components of Biktarvy. Biktarvy can increase the concentration of
drugs that are substrates of OCT2 or MATE1.

Drugs affecting renal function: Coadministration of
Biktarvy with drugs that reduce renal function or compete for active
tubular secretion may increase concentrations of FTC and tenofovir and
the risk of adverse reactions.

Pregnancy and lactation

Pregnancy: There is insufficient human data on the use of
Biktarvy during pregnancy. An Antiretroviral Pregnancy Registry (APR)
has been established. Available data from the APR for FTC shows no
difference in the rates of birth defects compared with a US reference
population.

Lactation: Women infected with HIV-1 should be instructed
not to breastfeed, due to the potential for HIV-1 transmission.

Dosage and administration

Dosage: 1 tablet taken once daily with or without food.

Renal impairment: Not recommended in patients with CrCl
<30 mL/min.

Hepatic impairment: Not recommended in patients with
severe hepatic impairment.

Prior to or when initiating: Test patients for HBV
infection.

Prior to or when initiating, and during treatment: As
clinically appropriate, assess serum creatinine, CrCl, urine glucose,
and urine protein in all patients. In patients with chronic kidney
disease, assess serum phosphorus.

INDICATION

Biktarvy is indicated as a complete regimen for the treatment of HIV-1
infection in adults who have no antiretroviral (ARV) treatment history
or to replace the current ARV regimen in those who are virologically
suppressed (HIV-1 RNA <50 copies per mL) on a stable ARV regimen for ≥3
months with no history of treatment failure and no known resistance to
any component of Biktarvy.

About Gilead Sciences

Gilead Sciences, Inc. is a research-based biopharmaceutical company that
discovers, develops and commercializes innovative medicines in areas of
unmet medical need. The company strives to transform and simplify care
for people with life-threatening illnesses around the world. Gilead has
operations in more than 35 countries worldwide, with headquarters in
Foster City, California.

For nearly 30 years, Gilead has been a leading innovator in the field of
HIV, driving advances in treatment, prevention, testing and linkage to
care, and cure research. Today, it’s estimated that more than 11.5
million people living with HIV globally receive antiretroviral therapy
provided by Gilead or one of the company’s manufacturing partners.

For more information on Gilead Sciences, please visit the company’s
website at www.gilead.com.

Forward-Looking Statement

This press release includes forward-looking statements within the
meaning of the Private Securities Litigation Reform Act of 1995 that are
subject to risks, uncertainties and other factors, including the risk
that physicians may not see the benefits of prescribing Biktarvy for the
treatment of HIV-1 infection and the possibility of unfavorable results
from additional clinical trials involving Biktarvy. These risks,
uncertainties and other factors could cause actual results to differ
materially from those referred to in the forward-looking statements. The
reader is cautioned not to rely on these forward-looking statements.
These and other risks are described in detail in Gilead’s Annual Report
on Form 10-K for the year ended December 31, 2018, as filed with
the U.S. Securities and Exchange Commission. All forward-looking
statements are based on information currently available to Gilead, and
Gilead assumes no obligation to update any such forward-looking
statements.

U.S. full Prescribing Information for Biktarvy, including BOXED
WARNING, is available at www.gilead.com.

Biktarvy, Gilead and the Gilead logo are trademarks of Gilead
Sciences, Inc. or its related companies.

For more information on Gilead Sciences, please visit the company’s
website at www.gilead.com,
follow Gilead on Twitter (@GileadSciences) or call Gilead Public Affairs
at 1-800-GILEAD-5 or 1-650-574-3000.